Question

Why do metals tend to lose electrons and nonmetals tend to gain electrons when forming ions?

Answer 1

Nonmetals tend to gain electrons in order to achieve a full outer shell, so they are said to have high electronegativities.

Alkaline metals, for example, would find it much easier to lose electrons than gain electrons, so they are not very electronegative. On the other hand, halogens such as chlorine only need to gain one electron to form a full outer shell. This is much easier than losing seven electrons instead.

When it comes to transition metals it is a little more complicated, but like many other metals, they also have low electronegativities.

Transition metals have `(n-1)d` and `ns` orbitals which have many electrons similar in energy, meaning that it is sometimes easy for many of those electrons to be lost. This is also the reason why metals have a high electrical conductivity (i.e. their electrons are can easily move from atom to atom).